Display devices should have high resolution, high response speed, low energy consumption, high transparency, and flexibility. These qualities depend on performances of thin film transistors (TFTs) used in the display devices. An amorphous silicon TFT has a relatively low carrier mobility, which cannot meet the requirements of high resolution and large area display. A low temperature poly-silicon (p-Si) TFT can have a high mobility. However, a high cost is incurred in creating a large area display device with the p-Si TFT. Recently, an amorphous oxide semiconductor, indium gallium zinc oxide (InGaZnO4, or IGZO), has been proposed. An IGZO based TFT has a high transparency, a low manufacturing temperature, and a good compatibility with the TFT manufacturing technology.
The mobility of the IGZO TFT is between that of the amorphous silicon TFT and the p-Si TFT, thus improvement is still required. An indium zinc oxide (IZO) device, with high carrier density and a low stability, is not a semiconductor but has a higher carrier mobility than that of IGZO.